Ok here goes... I did an extensive amount of reading people's grow journals tons of online cannabis articles. I can't tell you WHY the stems are hollow for sure, but I now know it has nothing to do with how it was grown (hydro or soil). Every article about hollow stems said that it was a characteristic of Sativa but even though this was said, I read plenty of grow journals about hybrids that were primarily indicia and had hollow stems.
There is one train of thought that if the grower really cares about what he is growing he will eliminate pith-filled stems from his grow, because hollow stems facilitate THC production. That isn’t to say that pith-filled stems do not, but a book called Marijuana Potency (Michael Stark) makes a connection between potency and stem structure. Stark says that this research has been backed by years and years of observation. So the hollow stems are sought after with groups of growers that follow this train of thought as pointed out by Stark’s book. (pith is just the fiber in the middle of the stem, the portion that is missing from the picture I posted above)
No matter how some species of plants are grown they are going to have fistular stems. In some species of plants hollow stems are caused my malnutrition or disease. This is not the case in cannabis/hemp. In a lot of water plants they have hollow stems to push oxygen down into the roots (that are under water) and also help the plant float. Again that statement was in regard to horticulture articles based on water plants and not cannabis.
Many of the articles I read said that all cannabis has hollow stems but some just has a very narrow hollowed area while others are very hollowed out. The latter was the sought after trait in Stark’s book. Most of the time when they referred to cannabis they specified sativa.
Most of the other message boards I was linked to said it was how the plant gets water to the buds, but I can't confirm that because none of the articles I read went into it. The only thing I can be sure of is that hollow stems have nothing to do with soil or hydroponics. Some believe it is sought after and others just think its just the normal course of cannabis growth.
-dirtybongwater
